Scientists have discovered a previously unknown single-celled organism in a California geothermal environment that is capable of growing and reproducing at temperatures previously considered beyond the known limits of complex life.

Named Incendiamoeba cascadensis, the organism was discovered in a hot-spring system within Lassen Volcanic National Park. Laboratory experiments showed that it could continue dividing at 63°C (145°F), establishing a new recorded upper temperature limit for eukaryotic life.

A Remarkable Survivor

The newly identified organism is an amoeba, a type of microscopic life capable of changing its shape as it moves and feeds.

Unlike bacteria and archaea, amoebae are eukaryotes, meaning their cells contain a nucleus and other membrane-bound structures. Eukaryotic organisms include animals, plants, fungi and many microscopic organisms.

For decades, scientists had generally regarded around 60°C as the upper boundary for sustained growth among eukaryotes. The discovery of I. cascadensis pushes that known boundary several degrees higher.

Discovered in a Volcanic Hot Spring

Researchers collected samples from geothermal streams in Lassen Volcanic National Park between 2023 and 2025.

The sampling locations contained water temperatures ranging from roughly 47°C to 64°C. Among the organisms collected, one unidentified amoeba showed unusual resistance to heat.

Back in the laboratory, researchers gradually increased the temperature surrounding the organism. It continued growing at temperatures around 57°C and eventually demonstrated active cell division at 63°C.

The researchers named the organism Incendiamoeba cascadensis, a name referring to both its heat-loving nature and the Cascade region where it was found.

It Does More Than Simply Survive

One of the most important aspects of the discovery is that the amoeba does not merely tolerate extreme heat for a short period.

At 63°C, researchers observed the organism undergoing mitosis—the process through which a eukaryotic cell divides to produce new cells. This demonstrated that it could remain biologically active and reproduce at that temperature.

At approximately 64°C, the organisms could still move and remain active.

When temperatures reached around 70°C, however, the amoebae changed their strategy. Instead of continuing normal activity, they formed protective outer structures and entered a dormant state. After being returned to cooler conditions, they were able to recover.

How Does It Handle Such Heat?

Researchers are investigating the molecular mechanisms behind the organism’s remarkable resilience.

Genomic analysis identified genes associated with protein maintenance and DNA repair. These biological systems may help the organism protect its cellular machinery from damage caused by extreme temperatures.

Scientists also observed physical changes in the amoeba when temperatures became more extreme. Its ability to alter its shape and form a protective layer appears to be another part of its survival strategy.

The precise mechanisms are still being studied, so researchers are not yet able to explain every aspect of its heat resistance.

It Has a Unique Ecological Advantage

Extreme heat may actually provide this amoeba with an unusually favourable environment.

Most organisms cannot survive at such temperatures, meaning the hot spring has fewer potential competitors. The amoeba feeds on heat-adapted bacteria and can occupy an ecological niche where many other organisms cannot function.

Researchers say its extreme heat tolerance may also reduce exposure to organisms that would normally prey on amoebae.

In other words, an environment that appears hostile to life may provide this microscopic predator with relatively little competition.

Not the Hottest Life on Earth

The discovery does not mean Incendiamoeba cascadensis is the hottest organism known.

Some bacteria and archaea—organisms with simpler cell structures—can survive and reproduce at considerably higher temperatures. The archaeon Methanopyrus kandleri, for example, can grow at temperatures around 122°C.

The significance of the new amoeba is that it belongs to the eukaryotic branch of life, whose cells are considerably more complex.

Implications for the Search for Life

The discovery could also influence the scientific search for life in extreme environments.

Researchers studying the origins and limits of life often examine places where temperature, pressure, radiation or chemistry would normally make survival difficult.

If complex cells can function at temperatures higher than previously documented, scientists may need to reconsider which environments are potentially suitable for microscopic life.

This does not provide evidence of extraterrestrial life. Instead, it expands scientists’ understanding of the environmental conditions under which complex biology can operate.

Potential Scientific and Industrial Applications

The organism could eventually become interesting beyond evolutionary biology.

Molecules that remain stable under extreme heat can have potential applications in biotechnology and industrial processes. Researchers at Syracuse University note that studying the organism could provide clues for developing heat-stable enzymes and other materials capable of functioning under demanding conditions.

However, any practical applications remain a subject for future research. Scientists first need to identify exactly which biological mechanisms allow the amoeba to remain functional under such extreme conditions.

A New Question About the Limits of Life

The discovery challenges a long-standing assumption about the thermal limits of eukaryotic organisms.

Rather than establishing a final boundary, the researchers say the finding raises another question: Are there other complex organisms capable of surviving at even higher temperatures?

Scientists plan to examine the amoeba’s relatives and investigate additional geothermal environments to determine how widespread these adaptations might be.

The discovery of Incendiamoeba cascadensis therefore represents more than the identification of a new species. It demonstrates that Earth’s microscopic ecosystems can still contain organisms with biological capabilities that scientists have not previously documented.

A tiny organism living in a volcanic hot spring has effectively expanded the known temperature range of complex life—and may encourage researchers to look in other extreme environments for similarly unexpected forms of biology.